This application claims priority to and the benefit of Japanese Application Ser. No. 2000-239777, filed Aug. 8, 2000.
This invention relates to a continuous strip casting device and to a method for the use thereof.
FIG. 5 illustrates the continuous strip casting device revealed by JP 8-300108 (and also U.S. Pat. Nos. 5590701 and 5960856), such continuous strip casting device being provided with a pair of casting rolls 101a and 101b that are rotatably supported in such a manner as to be juxtaposed horizontally parallel to each other and as to form roll gap G, with the outer circumferential surfaces of the casting rolls facing the said roll gap G. A molten metal supply means 102 of the casting device supplies molten metal to and between the casting rolls 101a and 101b, and a strip guide means 112 guides sideways the strip 103 that emerges from the roll gap G through the rotation of the casting rolls 101a and 101b. A pinch roll stand 105 grips the strip 103 that has passed from the strip guide means 112. An enclosure wall 107 provides a chamber 106 that is positioned below the casting rolls 101a and 101b and encloses the moving path for the strip 103 from the roll gap G to the pinch roll stand 105, with a scrap box 108 whose upper edge is in contact from below with the edge of the chamber 106 of the enclosure wall 107.
The outer circumferential surfaces of the casting rolls 101a and 101b are cooled by means of the cooling water that flows through the interiors of the casting rolls and the solidification of the molten metal on the surfaces of the casting rolls 101a and 101b is accelerated thereby.
Moreover, an actuator (not shown) that holds in close proximity the rotational axes of the casting rolls 101a and 101b is attached in order to regulate the roll gap G, and in turn the gauge of the strip 103 that is to be manufactured.
The molten metal supply system 102 also possesses a tundish 109 that receives the molten metal, and a nozzle 110 that pours the molten metal from the said tundish 109 to and between the casting rolls 101a and 101b. 
The strip guide means 112 is comprised of a support shaft 111 that is disposed below the casting roll 1010b and that is pivoted parallel to the said casting roll 101b, and a plurality of guide rolls 113 that are disposed laterally and that support the strip 103 that is transported sideways by the movable apron 112A.
The pinch roll stand 105 possesses a housing 114 through which the strip 103 passes, and a pressure roll 115a that is so mounted in the housing 114 as to come into contact with the lower surface of the strip 103, and a pressure roll 115b that is so mounted in the housing 114 as to come into contact with the upper surface of the strip 103.
The enclosure wall 107 is comprised of a steel outer shell 116 which is intended to impart support to an interior refractory lining 117 which extends across the entire inner surface of the outer shell 116.
A scrap box 108 is formed of refractory materials, and a seal member 118 is mounted in the top of the scrap box 10. The scrap box 108 is mounted on the car 121 that has wheels 120 that are able to move over the rails 119, and has a cylinder 122 that is able to raise the scrap box 108 as provided on the said car 121.
When strip 103 is manufactured by means of the continuous strip casting device illustrated in FIG. 5, the cylinder 122 attached to the car 121 raises the scrap box 108 bringing the upper edge of the scrap box 108 through the seal member 118 into contact with the edge of the chamber 106 of the enclosure wall 107. The leading edge of the movable apron 112A is so set as to be positioned below the support shaft 111. The distance between the rotational axes of the casting rolls 101a and 101b is set so that a roll gap G corresponds to the gauge of the strip 103 that is to be cast, and the casting rolls 101a and 101b are rotated in such a manner that their outer circumferential surfaces move from above towards the roll gap G.
Next, molten steel is supplied to the tundish 109, and when the molten steel is poured through the nozzle 110 to and between the casting rolls 111a and 101b, a solidified shell forms on the outer circumferential surfaces of the rolls, and as the casting rolls 101a and 101b rotate, the strip 103 is transported into chamber 106.
After the strip 103 has been presented in a laterally uniform state, the rotational axis of the casting rolls 101a and 101b rebounds in a very short time (approximately from 0.1 to 0.5 seconds) such that the roll gap G becomes approximately 1.5 to 3 times the thickness of strip 103, and then the roll gap G reverts to its original state. The expansion in the roll gap G causes the casting rolls 101a and 101b to produce areas of imperfect cooling, so that the strip 103 melts again through reheating effectively acting as a hot shear.
In this way, the strip 103 that is transported before the expansion of the roll gap G is broken off in a straight line from the strip 103 that is transported after the roll gap G has reverted to its original state, with the portion of the strip 103 that was remelted through the expansion of the roll gap G forming the boundary of the strip 103 to be transported to the coilers.
Moreover, the movable apron 112A is disposed laterally, and the strip 103 that is transported from the roll gap G after the break is led by the guide rolls 113 to the pinch roll stand 105.
The problem addressed by the present invention is that in the continuous strip casting device shown in FIG. 5, the space formed by the enclosure wall 107 that encloses the moving path for the strip 103 from the roll gap G to the pinch roll stand 105, and the scrap box 108 that comes into contact with the lower edge of the of the chamber 106 of the enclosure wall 107, is not filled with a non-oxidizing or weakly reducing atmospheric gas, and hence scale caused by oxidation develops on the strip 103.
Moreover, no means is provided for control of the flow of the atmospheric gas (air) between the casting rolls 101a and 101b and the movable apron 112A, and between the movable apron 112A and the guide rolls 113. The high temperature air that has been heated by the strip 103 blows in a concentrated manner onto the casting rolls 101a and 101b, while the insulating effect of the refractory lining 117 of the enclosure wall 107 impedes the cooling of the air within the chamber 106. This causes reheating of the strip 103 immediately after transport from the roll gap G and breakout and instability in casting. The high temperature strip 103 (not less than 1250xc2x0 C.) is transported to the pinch roll stand with scale, leading to embedded scale damage, and a likely reduction in yield.
Moreover, because the seal member 118 of the scrap box 108 is in contact with the edge of the enclosure wall 107 forming chamber 106, when an attempt is made to exchange the scrap box 108 during casting, a large amount of air flows into the chamber 106 causing severe strip oxidation. As a result, for practical purposes, it is not possible to exchange the scrap box 108 during the operation of the continuous strip casting device.
Moreover, splashes of molten metal and slag fall onto and accumulate on the seal member 118 between the enclosure wall 107 and the scrap box 108. As a result, the seal member 118 is deformed and damaged by the raising of the cylinder 122 of the scrap box 108 so that, each time the scrap box 108 is exchanged, the seal member 118 must be cleaned or replaced. Furthermore, it is difficult to restrict the inflow of external air and to maintain a low oxygen content inside the enclosing wall 107.
The present invention takes account of such deficiencies of the prior art, and enables the efficient manufacture of strip from molten steel with substantially reduced scale.
According to the invention there is provided apparatus for continuously casting metal strip comprising:
a pair of parallel casting rolls forming a nip between them;
a molten metal delivery system to delivery molten metal into the nip between the rolls to form a casting pool of molten metal supported on the casting roll surfaces immediately above the nip;
roll drive mechanism to drive the casting rolls in counter-rotational directions to produce a solidified strip of metal delivered downwardly from the nip between the casting rolls;
a casting chamber to enclose strip delivered downwardly from the nip;
a cooling chamber disposed below the casting chamber to receive the strip passing through the casting chamber from the nip through a transfer opening between the casting chamber and cooling chamber located beneath the nip between the casting rolls;
interchamber sealing system disposed at said transfer opening and having an open condition in which the opening is dilated and a closed condition in which the opening is contracted about the strip to enhance sealing between the casting and cooling chambers.
The apparatus may further comprise casting chamber gas inlet means to admit an oxidation inhibiting gas into the casting chamber. The oxidation inhibiting gas may be an inert gas or a weakly reducing gas.
There may be cooling chamber gas inlet to admit an oxidation inhibiting gas into the cooling chamber.
The interchamber sealing system may comprise a pair of seal rolls disposed on to either side of said transfer opening and a roll moving mechanism operable to move the sealing rolls between retracted positions and extended positions in which they contract the transfer opening.
The apparatus may further comprise a moveable scrap box to receive scrap strip at the bottom of the cooling chamber and a scrap box exchange chamber communicating with the bottom part of cooling chamber through an exchange opening closable by a moveable air tight door through which the scrap box can be moved in and out of its scrap receiving position at the bottom of the cooling chamber. The scrap box exchange chamber is provided with a moveable air sealing entry door through which the scrap box can pass into the exchange chamber, and with exchange chamber gas inlet through which to supply an oxidation inhibiting gas to the scrap box exchange chamber.
The apparatus may be further possess a heat exchange chamber with radiant tubes that are disposed in the heat exchange chamber. Guide rolls are disposed in the heat exchange chamber and transport laterally the strip that is sent from the cooling chamber. The heat exchange chamber is also provided with an atmospheric gas inlet.
The apparatus may also have a pinch roll chamber that communicates with the exit of the heat exchange chamber and that is able to receive the strip from the heat exchange chamber, and a partition door that is able to expand and contract in cross section the opening of the exit of the pinch roll chamber, and pinch rolls that are disposed in the pinch roll chamber and are capable of gripping the strip.
The apparatus may also have a rolling mill that is disposed in the downstream strip travel direction from the pinch roll chamber, and a strip pass line that runs from the exit of the pinch roll chamber to the rolling mill being typically so set as to lower the strip by between 10 mm and 150 mm for every 1 m distance of travel.
The invention further may provide a continuous strip casting device having a pair of casting rolls that form a roll gap and that are disposed parallel to each other in diametrical juxtaposition, and a molten metal supply system that supplies molten metal from above to and between the casting rolls, and a casting chamber that encloses the strip emerging from between the two casting rolls and in some embodiments the two casting rolls themselves, and an inter-chamber sealing system having a pair of seal rolls that permit the passage of the strip that is emerging from between the casting rolls downwards. A seal roll chamber may enclose the pair of seal rolls and communicate with or be within the casting chamber. A seal member slides the seal guide that is disposed in the seal roll chamber and positions the seal rolls in the path of and on either side of the strip in such a manner as to cause the movement of the seal rolls. A movable apron is so disposed as to guide sideways the strip that is transported downwards from between the seal rolls or alternatively to lower the said strip to a scrap box. The scrap box is disposed below the movable apron. A cooling chamber communicates with the inter-chamber sealing system and possesses an exit that is able to transport the strip that has been guided by the movable apron and that encloses the movable apron. An exit door is able to increase and decrease the cross section of the opening of the exit from the cooling chamber, and a scrap chamber possesses an air sealing door that is able to move the scrap box in and out of the cooling chamber and that encloses the scrap box that communicates with the cooling chamber, and in which the said casting chamber, cooling chamber and scrap chamber each possesses an atmospheric gas inlet.
The invention also provides a method of use of the continuous strip casting device, such method supplying an oxidation inhibiting gas such as a non-oxidizing or alternatively weakly reducing atmospheric gas, to the said casting chamber, cooling chamber and scrap chamber when strip is being continuously cast.